This project concerns identification of unusual patterns of cancer within specific occupational groups that may be indicative of exposure to hazards in the work environment. Study groups are selected for a variety of reasons including 1) known or potential exposure to established or suspect carcinogenic substances, 2) prior case reports and case-control studies suggesting an unusual cancer experience for the group, 3) availability of existing sources of data for defining a population-at-risk. Data sources include employment and death records maintained by companies, membership and death listings maintained by labor unions and professional organizations, and state licensing records. Studies underway include cohort mortality studies of persons employed in dry cleaning establishments, machinists, foundry workers and pest control operators. Proportionate mortality studies are being conducted for workers in the petrochemical industry and pharmaceutical and biological manufacturing, chromate painters, leather workers and metal workers.